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<title>Closure Unit Tests - goog.testing.PseudoRandom</title>
<script src="../base.js"></script>
<script>
  goog.require('goog.testing.PseudoRandom');
  goog.require('goog.testing.jsunit');
</script>
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<script>

  function runFairnessTest(sides, rolls, chiSquareLimit) {
    // Initialize the count table for dice rolls.
    var counts = [];
    for (var i = 0; i < sides; ++i) {
      counts[i] = 0;
    }
    // Roll the dice many times and count the results.
    for (var i = 0; i < rolls; ++i) {
      ++counts[Math.floor(Math.random() * sides)];
    }
    // If the dice is fair, we expect a uniform distribution.
    var expected = rolls / sides;
    // Pearson's chi-square test for a distribution fit.
    var chiSquare = 0
    for (var i = 0; i < sides; ++i) {
      chiSquare += (counts[i] - expected) * (counts[i] - expected) / expected;
    }
    assert('Chi-square test for a distribution fit failed',
        chiSquare < chiSquareLimit);
  }

  function testInstall() {
    var random = new goog.testing.PseudoRandom();
    var originalRandom = Math.random;

    assertFalse(!!random.installed_);

    random.install();
    assertTrue(random.installed_);
    assertNotEquals(Math.random, originalRandom);

    random.uninstall();
    assertFalse(random.installed_);
    assertEquals(originalRandom, Math.random);
  }

  function testBounds() {
    var random = new goog.testing.PseudoRandom();
    random.install();

    for (var i = 0; i < 100000; ++i) {
      var value = Math.random();
      assert('Random value out of bounds', value >= 0 && value < 1);
    }

    random.uninstall();
  }

  function testFairness() {
    var random = new goog.testing.PseudoRandom(0, true);

    // Chi-square statistics: p-value = 0.05, df = 5, limit = 11.07.
    runFairnessTest(6, 100000, 11.07);
    // Chi-square statistics: p-value = 0.05, df = 100, limit = 124.34.
    runFairnessTest(101, 100000, 124.34);

    random.uninstall();
  }

  function testReseed() {
    var random = new goog.testing.PseudoRandom(100, true);

    var sequence = [];
    for (var i = 0; i < 64000; ++i) {
      sequence.push(Math.random());
    }

    random.seed(100);
    for (var i = 0; i < sequence.length; ++i) {
      assertEquals(sequence[i], Math.random());
    }

    random.uninstall();
  }

</script>
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